The present invention relates to a silver halide photographic material. More particularly, the invention relates to a silver halide photographic material which contains a cyan coupler forming a stable dispersion and which produces a dye image of good keeping quality.
The mechanism behind the formation of dye images in a silver halide color photographic material is that an aromatic primary amine developing agent, while reducing silver halide grains in the exposed photographic material, is oxidized and the resulting oxidized product reacts with a coupler already present in the silver halide color photographic material so as to form a dye. Color reproduction in this case depends commonly on the subtractive process using three couplers which respectively form yellow, magenta and cyan dyes. These couplers are added to silver halide emulsion layers after they are dissolved in a substantially water-soluble high-boiling organic solvent, optionally in combination with an auxiliary solvent.
There are several requirements that must be met by the couplers: first, they must have high solubility in high-boiling organic solvents, and they should be highly dispersible in silver halide emulsions and the prepared dispersion should remain stable without causing the precipitation of the couplers; secondly, the couplers should provide good photographic characteristics; and thirdly, the couplers should produce dye images which are fast to light, heat and moisture.
One important question being raised recently by people in the photographic industry is how to improve the heat and moisture resistance (resistance to dark discoloration) of cyan couplers. Typical known cyan couplers are 2,5-diacylaminophenols having an acylamino group as a substituent on the 2- and 5-positions of the phenol ring, and cyan couplers of this type are shown in U.S. Pat. No. 2,895,826, as well as Japanese Unexamined Published Patent Publication Nos. 112038/1975, 109630/1978 and 163537/1980. Such 2,5-diacylaminophenolic cyan couplers are extensively used since they produce cyan dye images having high resistance to dark discoloration. However, the resistance to light discoloration of the produced dye image is extremely low, and the unreacted cyan coupler is highly likely to turn yellow upon exposure to light (this phenomenon is hereunder referred to as Y stain under light). In an extreme case, this low-density area of the image turns pink upon exposure to light, and this may amplify the visible discoloration of the image.
The use of a benztriazole compound (see, for example, Japanese Unexamined Published Patent Application No. 151149/1975) has been proposed as a means for improving the resistance to light discoloration of 2,5-diacylaminophenolic cyan couplers. However, this benztriazole compound is not suitable for use in practical applications since it has a great tendency to form a precipitate and is only effective against discoloration resulting from exposure to UV radiation. Using an increased amount of a conventional high-boiling organic solvent, such as dibutyl phthalate, is also known. This method is capable of achieving a slight improvement in resistance to light discoloration, but on the other hand, it produces an image with impaired photographic characteristics (e.g. tone) and low resistance to dark discoloration. As a further problem, this method is substantially ineffective in preventing the occurrence of Y stain upon exposure to light.
Japanese Unexamined Published Patent Application No. 173835/1982 proposes a method for providing an improved tone and a light-fast dye, and according to this method, a 2,5-diacylaminophenolic cyan coupler wherein the phenol ring is substituted at 2-position by an ortho-sulfonamidophenylacylamino group is dispersed with the aid of a high-boiling organic solvent having a specified dielectric constant. However, the cyan dye image produced by this method has an appreciably low resistance to light discoloration.